CN112539336A

CN112539336A - Recovery device for high purity or toxic fluid

Info

Publication number: CN112539336A
Application number: CN202011541512.0A
Authority: CN
Inventors: 张涛; 季向东; 刘江来
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2020-12-23
Filing date: 2020-12-23
Publication date: 2021-03-23

Abstract

The invention discloses a recovery device of high-purity or toxic fluid, which comprises an inner layer pressure container, a middle layer pressure container, an outer layer vacuum container, a thermal switch of the inner layer pressure container, pipelines and valves of all containers and the like; the inner layer pressure container is used for containing high-purity or toxic fluid media, an annular closed space formed by the middle layer pressure container and the inner layer pressure container can be filled with liquid nitrogen or other low-temperature fluids, the outer layer vacuum container can provide a vacuum environment to reduce heat leakage, and a thermal switch connected with a corrugated pipe is designed between the inner layer pressure container and the outer layer vacuum container and can be switched on and off on the premise of ensuring vacuum. When the middle-layer pressure container is filled with liquid nitrogen or other low-temperature fluid, the lower vapor pressure is obtained in the inner-layer pressure container, so that the recovery of high-purity or toxic fluid is realized. The invention has the advantages of convenient use, easy maintenance, rapid response, miniaturization and integration of equipment, and capability of being in a standby state for a long time.

Description

Recovery device for high purity or toxic fluid

Technical Field

The invention relates to the field of using high-purity or toxic fluid, which needs to be recycled due to high price or cannot be randomly discharged due to toxicity or harm in industrial production or scientific experiments, in particular to a recovery device of the high-purity or toxic fluid, which is suitable for the fluid recovery field.

Background

In the liquid xenon dark substance detection experiment represented by PandaX, xenon with the purity of more than 99.9995 percent is needed, the content of krypton in the xenon is reduced to 1ppt or even 0.1ppt, and meanwhile, the price of the xenon is very high, so that high-purity xenon must be recovered after the experiment is finished, and in the experiment process, in order to prevent accidents, preparation for recovering the high-purity xenon must be made. One method of the existing xenon recovery technology is to utilize a diaphragm compressor to fill xenon into a gas cylinder or a pressure storage tank, but the diaphragm compressor requires that the inlet pressure is not less than 0.2MPa, and xenon below the pressure must be recovered by other technologies. The second method is to put the gas cylinder or pressure storage tank in an open Dewar, then fill liquid nitrogen for cooling, the xenon gas is condensed or desublimated on the inner surface of the gas cylinder or pressure storage tank, and the thermal resistance of the condensed or desublimated xenon is increased along with the proceeding of the recovery process, thereby the recovery rate is synchronously reduced. This method has three disadvantages, which cause more difficulty in the operation and maintenance of the experimental apparatus. Firstly, liquid nitrogen in an open Dewar is volatilized quickly, injected liquid nitrogen is consumed quickly, most of the time, the Dewar and an internal gas cylinder or a pressure storage tank are at room temperature, and an additional device is needed for supplying the liquid nitrogen; secondly, the liquid nitrogen is injected into the Dewar from the beginning until the gas cylinder or the pressure storage tank has recovery capability, so that the recovery time is long, the transient recovery capability is unavailable, and the dynamic response characteristic is poor; thirdly, the liquid nitrogen in the dewar is at the bottom, the condensed liquid xenon on the inner surface of the gas cylinder or the pressure storage tank can be collected at the bottom, the position which needs to be cooled most at this moment is the middle upper part of the gas cylinder or the pressure storage tank, namely the liquid nitrogen can not effectively cool the gas cylinder or the pressure storage tank, the effective utilization rate of the liquid nitrogen is low, and the liquid nitrogen is inconvenient in a closed underground laboratory space or on occasions where the liquid nitrogen is difficult to obtain.

Disclosure of Invention

In order to solve the technical problems and optimize the operation stability and reliability of the PandaX dark substance detection experiment system, the invention provides a recovery device of high-purity or toxic fluid, which can conveniently recover xenon and is in a standby state for a long time.

The technical solution of the invention is as follows:

a recovery unit of high-purity or poisonous fluid, wherein include the inner layer pressure vessel that can bear the internal pressure and external pressure in the centre, and the middle layer pressure vessel that is fitted over the outer pressure vessel of this inner layer, make the inner layer pressure vessel and form the inner closed space between the middle layer pressure vessels, the said middle layer pressure vessel is placed in the outer vacuum vessel, make the middle layer pressure vessel and form the outer closed space between the outer vacuum vessels;

a fluid coil pipe is uniformly distributed on the outer surface of the inner-layer pressure container, one end of the fluid coil pipe extends out of the outer-layer vacuum container through a coil pipe valve, and the other end of the fluid coil pipe is communicated with the inner closed space;

a first valve and a pipeline are introduced into the inner closed space through the outer layer vacuum container, a second valve and a pipeline are introduced into the inner closed space through the outer layer vacuum container, a third valve and a pipeline are introduced into the inner layer pressure container through the outer layer vacuum container and the middle layer pressure container, a fourth valve and a pipeline are introduced into the inner layer pressure container through the outer layer vacuum container and the middle layer pressure container, and a rupture disk and a pipeline are introduced into the inner layer pressure container through the outer layer vacuum container and the middle layer pressure container; the safety valve and the liquid level meter are respectively introduced into the middle-layer pressure container through the outer-layer vacuum container.

The inner layer pressure container is provided with 3 sets of valves and pipelines, the 1 st set of valves and pipelines is used for gas to enter and exit, and one end of each pipeline is opened at the upper part of the inner layer pressure container; the 2 nd set is a rupture disk, and the other end of the pipeline is opened at the upper end of the inner pressure container; the 3 rd sleeve can be used for liquid discharge, and one end of the pipeline is opened at the bottom of the inner pressure container.

The middle-layer pressure container and the inner-layer pressure container form an annular closed space, the space is provided with 4 sets of pipelines and valves which lead to the outside of the equipment, the opening of the No. 1 pipeline is arranged near the middle part of the closed space, the No. 2 pipeline is a cooling coil, the opening of the No. 3 pipeline is arranged at the upper part of the closed space, the No. 4 pipeline is a safety valve, and the opening of the pipeline is arranged at the upper part of the equipment; the cooling coil is wound on the outer side of the inner-layer pressure container, fluid flowing through the cooling coil can directly contact with the shell of the inner-layer pressure container for heat exchange, the upper part of the cooling coil reaches the outside of the equipment through the heat insulation vacuum layer, a valve is arranged on a pipeline, and the lower end of the cooling coil is opened at the bottom of the closed space; in the process of recovering the medium, the 1 st set and the 3 rd set of pipelines and valves are closed, part of liquid nitrogen or other low-temperature fluid is gasified by absorbing heat from the inner-layer pressure container of the recovery device, the air pressure of the middle-layer pressure container is increased, the liquid nitrogen or other low-temperature fluid is driven to enter the 2 nd pipeline, and is gasified and discharged after exchanging heat with the inner-layer pressure container of the recovery device, so that the heat exchange area of the inner-layer pressure container of the recovery device is fully utilized; if the air pressure in the middle-layer pressure container is too high, partial pressure is released through the safety valve, the safety of the device is ensured, and waste of liquid nitrogen is avoided.

The outer layer vacuum container provides a vacuum heat insulation environment of the inner layer pressure container and the middle layer pressure container, and the vacuum layer is provided with a valve for connecting a vacuum pump;

the inner-layer pressure container is an upper contact of the thermal switch, a lower contact of the thermal switch is connected with the wall of the outer-layer vacuum container through a corrugated pipe, the lower contact of the thermal switch can be driven by the jack structure below to move up and down, and the thermal switch is closed and opened on the premise of not damaging vacuum, so that the heat input control of the inner-layer pressure container is realized. The jack structure can realize the lifting function by adjusting the screw rod;

the lower contact of the thermal switch is connected with the outer layer vacuum container through a corrugated pipe, can move up and down on the premise of ensuring vacuum, and is closed or disconnected with the upper contact of the thermal switch so as to obtain the expected heat transfer function or heat insulation function; the lower contact of the thermal switch is connected with the outer vacuum container through a flexible heat transfer structure or a heat pipe so as to ensure the heat transfer capacity of the thermal switch;

the up-and-down movement of the lower contact of the thermal switch is realized by adjusting a jack structure consisting of the hinge with the threads, the hinge, the positive and negative threaded rods on the two sides and the rod piece, two of the bottoms of the hinges are fixed with the bottom plate, and the bottom plate is fixed at the bottom of the outer layer vacuum container shell;

one end of the heat conductor is fixed on the lower contact of the thermal switch, and the other end of the heat conductor is fixed at the bottom of the outer layer vacuum container shell and used for enhancing heat transfer;

the outer side of the inner layer pressure container is provided with a space for containing the low-temperature fluid, the bottom of the inner layer pressure container is provided with a thermal switch upper contact and a thermal switch lower contact, and the low-temperature fluid space is insulated from the outside by vacuum;

the lower end opening of the fluid coil pipe is away from the bottom of an annular closed space formed by the middle-layer pressure container and the inner-layer pressure container and accounts for 1/3 in the total height of the annular closed space.

The principle of the invention is as follows:

as is clear from the xenon gas-solid-liquid three-phase diagram, the lower the temperature is, the lower the saturated vapor pressure of the medium is at the critical temperature or lower, and therefore, the recovery function can be realized as long as the temperature of the inner pressure vessel of the high-purity or toxic fluid recovery apparatus is lower than the temperature of the experimental facility. When the inner-layer pressure container of the recovery device and the low-temperature cooling liquid realize heat balance, the air pressure of the residual gas of the experimental equipment is finally consistent with the saturated vapor pressure of xenon corresponding to the temperature of the inner-layer pressure container of the recovery device. For example, xenon gas has a freezing point of 161K and a boiling point of 165K in a 1atm environment, and if the temperature of the inner pressure vessel of the recycling apparatus is 165K, xenon gas of 1atm remains in the experimental apparatus, about 6kg/m³Considering the xenon gas price, this equilibrium gas pressure is unacceptable and continued cooling is required to achieve a lower gas pressure equilibrium point. When the temperature of the liquid nitrogen is-196 ℃, the saturated vapor pressure of xenon is lower than 1Pa, the residual xenon amount is extremely small, and the xenon recovery task is considered to be finished.

The prior recovery device places a xenon bottle or a xenon storage tank in an open Dewar with liquid nitrogen, and has the following problems along with the recovery: first, the recovered medium is desublimated to a solid state and attached to the inner wall of the inner pressure vessel of the recovery device, and the thermal resistance from the outer wall of the inner pressure vessel to the medium is increased. Secondly, the condensed liquid medium is collected to the bottom of the inner-layer pressure container under the action of gravity and is possibly further cooled to be solid, liquid nitrogen outside the inner-layer pressure container is gradually consumed in the medium recovery process, and the liquid level is gradually reduced, so that the recovery capacity of the upper half part of the inner-layer pressure container is gradually reduced to a negligible degree; meanwhile, the thermal resistance of the recovered medium at the lower half part of the inner-layer pressure container is increased more quickly, and the recovery capacity is also reduced quickly. Thirdly, the pressure difference between the internal pressure of the inner layer pressure container of the recovery device and the experimental equipment is smaller and smaller, so that the recovered mass flow is smaller and smaller, and a longer time is needed in the final stage of recovery.

Compared with the prior art, the invention has the beneficial effects that:

firstly, the xenon gas cylinder or the storage tank and the Dewar device are made into an integral structure, so that the structure is more compact, the size is small, and the experimental equipment is convenient to arrange;

secondly, liquid nitrogen or other low-temperature fluids are stored in a closed space with good heat insulation and can be stored for a long time, namely the recovery device can be in a standby state for a long time, and the maintenance period is long, so that the automatic operation of the whole set of experimental device is guaranteed;

thirdly, the utilization rate of the cold energy of the liquid nitrogen or other low-temperature fluids is improved, which is significant for underground laboratory occasions which are difficult to obtain the liquid nitrogen and inconvenient to discharge a large amount of nitrogen;

fourthly, the effective heat exchange area in the recovery process is increased, so that the recovery rate is increased, and the safe operation and the high-efficiency operation of the experimental device are guaranteed.

Drawings

FIG. 1 is a schematic diagram of a high purity or toxic fluid recovery apparatus according to the present invention;

Detailed Description

Embodiments of the invention will be described in detail below with reference to the drawings, but the invention can be embodied in many different forms and defined by the claims.

Pretreatment before use: the inner layer pressure container 10 is used for containing high-purity or toxic fluid, and needs to be vacuumized to 1E-4Pa, or the vacuum degree is properly required according to the purity requirement of a working medium. To facilitate rapid release of the adsorbed gas from the inner surface of the inner pressure vessel 10, the fluid may be heated. There are 3 choices for the fluid inlet and outlet pipes and valves, the first valve and pipe 1, the coil valve 2 and fluid coil 11, the second valve and pipe 6. Fluid is injected from the first valve and the pipeline 1 or the second valve and the pipeline 6 and flows out from the fluid coil 11 and the coil valve 2, only less fluid is needed, and the space formed by the middle-layer pressure container 9 and the inner-layer pressure container 10 is not required to be completely filled, but the fluid coil 11 is uniformly distributed on the surface of the inner-layer pressure container 10, so that uniform heating can still be realized. If the flow is reversed, more fluid is required. And (3) heating the inner-layer pressure container 10 to a rated temperature by using fluid while vacuumizing until the vacuum degree meets the requirement, and preparing for subsequent use.

And (3) recovery working condition: opening the first valve and the pipeline 1 or the second valve and the pipeline 6, injecting liquid nitrogen into the space formed by the middle layer pressure container 9 and the inner layer pressure container 10 through the valves and the pipelines, wherein the structure temperature is high during the first injection, a large amount of liquid nitrogen is gasified, the pressure in the closed space is increased, and the injection flow needs to be strictly controlled until the closed space is filled. The first valve and line 1 and the second valve and line 6 are then closed. And connecting the third valve and the pipeline 3 of the inner-layer pressure container 10 with experimental equipment, vacuumizing the corresponding pipeline to prevent air from polluting xenon, and opening the third valve and the pipeline 3at any time to perform recovery operation when the vacuumizing interface is closed and the recovery device is in a standby state. The maintenance or replenishment cycle may be determined based on the daily boil-off data for the liquid nitrogen, or whether to replenish the liquid nitrogen may be determined based on the level gauge 22.

The heat leakage causes the liquid nitrogen to be gasified, so that the pressure is increased, and after the pressure exceeds the action pressure of the safety valve 21, the nitrogen is automatically released to the safety pressure and then closed until the nitrogen pressure exceeds the action pressure next time. If the flow rate of the recovered xenon is large, the vaporization amount of the liquid nitrogen is also large, so that the safety valve 21 is frequently operated, and the second valve and the pipeline 6 can be opened to release the nitrogen. If the recovery rate is lower than the expected value after the recovery operation is carried out for a period of time, the first valve and the pipeline 1, the second valve and the pipeline 6 can be closed, the gasified nitrogen gas pressurizes the closed space, the liquid nitrogen is forced to cool the upper part of the inner-layer pressure container 10 through the fluid coil pipe 11, and the liquid nitrogen can be supplemented through the first valve and the pipeline 1at the same time until the recovery operation is finished.

In this case, the liquid xenon may be directly recovered through the third valve and the pipe 3, and the liquid xenon flows into the bottom of the inner pressure vessel 10 or solidifies during the flow along the inner surface. The liquid xenon has high density and much lower heat of fusion than heat of vaporization, so the recovery efficiency of the liquid xenon is higher.

Liquefaction working conditions: the liquid xenon required by the PandaX dark substance detection experiment works at 2-3 atm and near-95 ℃, can be liquefied in advance by using the device, and then is directly injected into the detector, so that the experiment process is accelerated. The freezing point of the absolute ethyl alcohol is-114 ℃, and the refrigerator using the absolute ethyl alcohol as the refrigerating medium can stably output at any temperature of-90 ℃ to-110 ℃. The low-temperature ethanol output by the refrigerator can circulate and cool the inner-layer pressure container 10 through any two sets of the first valve and the pipeline 1, the coil valve 2 and the fluid coil 11, and the second valve and the pipeline 6, so that the xenon gas is liquefied on the inner surface.

When liquid xenon needs to be output, the fourth valve and the pipeline 5 are connected with experimental equipment, then xenon with relatively high pressure is introduced through the third valve and the pipeline 3, or the upper contact 12 of the thermal switch and the lower contact 13 of the thermal switch are closed to increase heat input, the pressure of the inner-layer pressure container 10 is increased, and the liquid xenon is input into the detector through the fourth valve and the pipeline 5.

Heating working conditions are as follows: after the xenon is recovered by the liquid nitrogen, the xenon in the inner pressure vessel 10 is in a solid state for a short time, and cannot be output to the outside. Or the xenon gas can not be output when the gas pressure on the surface of the liquid xenon is low. The thermal input can be increased by adjusting the jack screw 16 to close the upper thermal switch contact 12 and the lower thermal switch contact 13.

The application of the invention is not limited to xenon, and other high-purity or toxic or other fluids which need to be recycled or cannot be discharged can be recycled. The specific recovery temperature can be determined according to specific parameters such as boiling point, freezing point and vapor pressure of the working medium.

Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims

1. The recovery device of high-purity or toxic fluid is characterized by comprising an inner layer pressure container (10) with the center capable of bearing internal pressure and external pressure, and a middle layer pressure container (9) sleeved outside the inner layer pressure container (10), wherein an inner closed space is formed between the inner layer pressure container (10) and the middle layer pressure container (9), the middle layer pressure container (9) is placed in an outer layer vacuum container (8), and an outer closed space is formed between the middle layer pressure container (9) and the outer layer vacuum container (8);

a fluid coil pipe (11) is uniformly distributed on the outer surface of the inner-layer pressure container (10), one end of the fluid coil pipe (11) extends out of the outer-layer vacuum container (8) through a coil pipe valve (2), and the other end of the fluid coil pipe is communicated with the inner closed space;

a first valve and a pipeline (1) are communicated with the inner closed space through the outer layer vacuum container (8), a second valve and a pipeline (6) are communicated with the inner closed space through the outer layer vacuum container (8), a third valve and a pipeline (3) are communicated with the inner layer pressure container (10) through the outer layer vacuum container (8) and the middle layer pressure container (9), a fourth valve and a pipeline (5) are communicated with the inner layer pressure container (10) through the outer layer vacuum container (8) and the middle layer pressure container (9), and a rupture disk and a pipeline (4) are communicated with the inner layer pressure container (10) through the outer layer vacuum container (8) and the middle layer pressure container (9); a safety valve (21) and a liquid level meter (22) are respectively introduced into the middle-layer pressure container (9) through the outer-layer vacuum container (8).

2. The recovery apparatus for high purity or toxic fluid according to claim 1, wherein the first valve and pipe (1) has a longer length than the second valve and pipe (6), and the first valve and pipe (1) has a port located at the lower portion of the inner closed space, and the second valve and pipe (6) has a port located at the upper portion of the inner closed space.

3. The recovery apparatus for highly pure or toxic fluid according to claim 1, wherein the fourth valve and pipe (5) is longer than the length of the third valve and pipe (3), the port of the fourth valve and pipe (5) is located at the lower part of the inner pressure vessel (10), and the port of the third valve and pipe (3) is located at the upper part of the inner pressure vessel (10).

4. The apparatus for recycling highly pure or toxic fluid as claimed in any one of claims 1 to 3, wherein the bottom of the inner pressure container (10) is provided with a thermal switch upper contact (12), a thermal switch lower contact (13) is connected with the outer vacuum container (8) through a bellows (14), the thermal switch lower contact (13) is moved up and down by adjusting a driving device composed of a hinge (15) with threads, a hinge (18), double-sided positive and negative threaded rods (16) and a rod member (19), and the bottom of the outer vacuum container (8) is provided with a bottom plate (17) for placing the driving device.

5. The apparatus for recycling of highly pure or toxic fluid according to claim 4, further comprising a heat conductor (20), wherein one end of the heat conductor (20) is connected to the lower contact (13) of the thermal switch and the other end is connected to the base plate (17).

6. The apparatus for the recovery of highly pure or toxic fluids according to any of claims 1 to 3, further comprising evacuation valves and pipes (7) with one end opening into said outer vacuum vessel (8) and the other end connected to a vacuum pump.

7. The apparatus for the recovery of highly pure or toxic fluids according to claim 1, wherein the other end of the fluid coil (11) is connected to the bottom of the inner closed space where the orifice of the inner closed space is located and occupies 1/3 of the total height of the inner closed space.